Estimation of micro-size defects in electrolyte thin-film by X-ray stress measurement for anode-supported solid oxide fuel cells

Abstract

For anode-supported solid oxide fuel cells (SOFCs), huge internal stress is generated in an electrolyte thin-film due to the difference of the coefficient of thermal expansion from an anode substrate. Micro-size defects are sometimes formed in the electrolyte thin-film during a manufacturing process, when the huge internal stress is released. The defects in the electrolyte thin-film cause cross leakage of fuel and air, which deteriorate the anode-supported SOFCs rapidly. The mechanical reliability of the electrolyte thin-film is important to prevent initial failure for cells and stacks. In the present work, the internal stress was evaluated by X-ray for planar anode-supported SOFCs with and without micro-size defects in an electrolyte thin-film. A compressive stress of 501-561 MPa was observed for yttria-stabilized zirconia (YSZ) electrolyte thin-film without micro-size defects on NiO-YSZ anode substrate sintered at 1350-1400 ℃. However, the stress was 188 and 453 MPa for the electrolyte thin-films sintered at 1200 and 1300 ℃, respectively, because of insufficient sintering. Many micro-size cracks and pores were observed in the electrolyte thin-films sintered at 1200 and 1300 ℃. Furthermore, the internal stress decreased by 50-100 MPa due to stress relief for the electrolyte thin-film with micropores, which were made during the actual manufacturing process, in spite of the sintering temperature of 1350 ℃. X-ray stress measurement has a potential to be applied as a non-destructive test method for anode-supported SOFCs.

Keywords

• solid oxide fuel cell (sofc)
• x-ray stress measurement
• micro-size defect
• electrolyte thin-film
• yttria-stabilized zirconia (ysz)